The
combination of unprecedented resolution and light gathering
power will not only provide unique images of objects at all
scales of the universe, from planets to clusters of galaxies,
it will also allow their detailed spectral analysis, thus revealing
their nature, kinematics and characteristics.

As the light we receive from distant
objects had to travel considerable distances, the further we
probe into the universe, the younger we see it. Peering into
the deep universe is akin to reading a whole "biography"
from birth to old age, with tantalizing glimpses on its conception.

Universe
or Universes ?

Most theories of the
earliest universe require an initial set of 10 or so spacetime
dimensions. The majority of these "compactified" at
an early time, reducing the effective number to the present
four (time and space), over a short time during which various
"constants" of nature converged towards their present
values. If we can observe suitable phenomena at epochs so early
that the extra dimensions were not yet negligibly small, deviations
from present-day values of these "constants" (including
the fine-structure constant, the proton-to-electron mass ratio,
the gravitational constant and the speed of light) should become
apparent. Different theories predict different rates of change
for different fundamental physics "constant". Some
theories even postulate multiple Universes. OWL may allow -perhaps-
the first experimental investigation of whether our Universe
is unique or not by reaching deep into its past.

Engines
of change: the first stars ?

In its early ages our Universe was opaque. After a mere 400
million or so, the first sources of intense radiation -possibly
the first generation of stars and/or super-massive black holes-
almost fully re-ionized it. By way of nuclear fusion, stars
burn light elements into heavier ones, thereby progressively
enriching the chemical distribution of elements in the universe.
The first generation of stars did not hav e any heavy element,
and as a result were markedly hotter, and shorter-lived than
their successors. They also carry a distinct spectroscopic
signature, quite different from that of present ones. A telescope
the size of OWL is required to detect and analyze this primordial
stars and the galaxies they formed, and find out which were
the sources of re-ionization. It will do so, not only in visual
and near-infrared wavelengths, but also at mm wavelengths,
looking at dust-shrouded stars and galaxies which contribute
to about half of the total stellar energy output in the whole
Universe.

GALAXIES

Galaxies
are the essential "building blocks" of the visible
part of our Universe. They come in a wide range of sizes, morphologies,
and stellar populations. Their nuclei may host some of the most
energetic physical processes by which a volume of space smaller
than the Sun can outshine the entire Universe for a few seconds.
They have been detected to the farthest reaches accessible to
modern telescopes, yet only the nearest can be resolved into
stars and analyzed properly. OWL will be able to resolve stars
at much larger distances an in particular peer into the purely
stellar elliptical galaxies, now almost devoid of any gas, and
all too far from us with present observing capabilities.

Cannibals
in the sky

Simulation of a patch of the Universe at early times,
(B. Moore, Institute for Theoretical Physics, Zurich).

As our Universe began its first five hundred million years of
existence, the delicate cosmic tapestry of galaxies began to
form. Driven by dark matter seeds planted at its very birth,
intense star-forming regions appeared along titanic-size "walls"
connected to each other like in soap-bubble foam. In those early
days, when the Universe was but a fraction of its present size,
these groups of proto-galaxies were closely packed and thus
intensely interacted through gravitational attraction. True
to age-old human experience, during this ferocious cannibalism
stage, the bigger galaxies swallowed the smaller ones, becoming
even fatter in the process and evolving into the giant galaxies
of today, such as our own Milky Way. OWL will be able to study
myriads of galaxies caught in the full act at meal time and
will quantitatively gauge how this process has shaped the visible
Universe.

PLANETS

In the past few years,
exoplanets have been discovered at an increasing rate, with
already more than 100 identified. No direct observation is possible
with existing telescopes; the existence of these planets is
generally inferred from the minute perturbation of their parent
star's motion. Closer to us, solar system objects are periodically
visited by space probes, which provide spectacular but short
snapshots of our neighborhood. Those limitations will no longer
hold with OWL.

Exoplanets
and extraterrestrial life

Perhaps the Holy
Grail of present-day astronomy would be the detection of biomarkers
on earth-like, or perhaps even not earth-like, planets around
other stars. This is being attacked with both flotillas of free-flying
satellite interferometers in space or single giant telescopes
on the ground. Both approaches are technically hugely challenging
and clearly very long-term; yet they are bound to be pursued
in earnest by most major astrophysical projects and, certainly,
by OWL.

A
flyby every night

Much closer to our
home planet, in a mere fraction of a second, OWL will be able
to get the same crisp view of the clouds in the atmosphere of
solar-system planets, volcanoes on Io or transient ringlets
around Saturn, as a man-made flyby probe. Contrary to such probes,
regular meteorological and geophysical studies of these continuously
evolving phenomena will be possible over long time scales .
at extremely low cost.

WALKING
INTO THE UNKNOWN

After the known unknowns,
the unknown ones. It is a constant historical trait that telescopes
became famous not for what they were built for, but for totally
unexpected discoveries that opened entire new chapters of astrophysics.
As one of many examples, the 3.6 m telescopes at La Silla and
Hawaii were developed in the 70s, the first to refine stellar
evolution through studies of the Magellanic Clouds and the second
to detect fainter farther galaxies. Yet both teamed to unexpectedly
discover gravitational arcs in clusters of galaxies, which besides
being a beautiful example of gravitational optics, constitute
the gauge to weigh individual galaxies, clusters of galaxies
and even the whole Universe, which was sorely lacking in the
astronomer toolbox. We may expect, or at least hope, more of
the same from OWL!